Which sub to match B&W CM 8 and company?

Just purchased some B&W CM 8's with matching center and rear in ceilings for a 5.1 setup. I don't want to spend more than 1,500 for a sub. I am considering HSU research (two 15') and SVS ultra 13'. Do you think these will compliment the other speakers? Any thoughts on other subs or any ideas? Do I get 1 or 2 subs? Too many options...Thanks